I recently got great prices and delivery from CP Performance.
If it it OEM that you want check to make sure they are Mercruiser part numbers in your kit.
They also sell the Sierra and others too. Do you have a dry joint system?

I would only use mercruiser parts.
Dont skimp out on the most important part of the motors( the cooling system.)
They're inboards so they're probably not dry joints.
Don't forget the spacers too they're probably 3 inch
I did mine last season 2K for all mercruiser parts from Lighthouse Marine
marineengineparts.com